1. Field of the Invention
The present invention relates in general to ducting structures for turbine engines, and methods for making same.
2. Background Art
Gas turbine engines, especially those for aircraft propulsion applications, utilize ducts for drawing air flow from one portion of the engine, e.g., for providing a source of cooling air, which air flow must then be returned to another portion of the engine.
One such structure which requires ducting is known as the air oil cooler (for cooling the lubricating oil for the engine). This device requires an inlet duct, which guides cooling air, from a forward (inlet) part of the turbine from the fan stream through the air oil cooler. At the downstream side of the cooler heat exchanger structure, an outlet duct guides the “used” cooling air back into the fan stream.
The ducts which service the air oil cooler (and other such engine ducting structures) typically must be able to address several design parameters: 1) the ducts must withstand temperatures ranging from approximately −65° F. to approximately 700° F.; 2) the ducts must withstand relatively low pressure, e.g., approximately 8-18 psig; 3) the ducts must be fireproof and/or fire resistant; 4) the ducts must be resistant to vibration; 5) the ducts must be non-flammable; and 6) the ducts should be as light as possible.
Such intra-engine ducting structures have typically been formed as wholly metallic structures, often fabricated from one or more high-performance materials, such as corrosion-resistant stainless steel (Cres) or titanium.
For example, Peyton et al., U.S. Pat. No. 3,911,961 discloses multilayer ducting for high temperature ducts for aircraft, including an outer insulating sleeve formed from a sandwich of metal foil and resin-impregnated cloth and an inner metal duct, separated by an air gap. Fischer et al., U.S. Pat. No. 4,934,412 discloses a cooling pipe line for a turbine engine, having a load-bearing inner layer of heat-curable, fiber-reinforced resin, surrounded by a heat insulating layer of heat-curable, fiber-reinforced resin.
Norek, U.S. Pat. No. 7,047,615 B2 discloses a method for making turbine engine transition duct bodies without longitudinal welds by hydroforming two duct bodies back to back with bellows thrusters secured to the duct body open ends. This enables the manufacturing of duct bodies with detailed features and high pressure without using compression cylinders. Multi-layer transition duct bodies can also be assembled with layers of different materials, for example, having a heat-resistant layer inside and high strength layer outside. They can be assembled using cold shrinking and heat expanding. In addition, anti-fretting and anti-vibration coatings can be applied between the layers for improved performance.
It would be desirable to provide a ducting structure, e.g., for gas turbine engines, which is lightweight, durable, and resistant to heat, fire and vibration.
These and other desirable characteristics of the invention will become apparent in view of the present specification, including the claims, and drawings.